Patent GB-741641-A (GB)
Title: Improvements in or relating to torque limiting full power control systems for airplanes
Inventor: FEENEY THOMAS AQUINAS
IPC: B64C13/24
Filed: 1953-10-01
Abstract: 741,641. Aircraft controls. NORTHROP AIRCRAFT, Inc. Oct. 1, 1953, No. 26951/53. Class 4. [Also in Group XXIX] A full powered aeroplane surface control system in which a hydraulic motor adapted to move the surface is energized in accordance with control means is characterized in that the hydraulic motor is reversible by the surface, and that means are connected to the hydraulic source to limit its maximum pressure to a value where the maximum force applicable by the motor to the surface does not exceed the safe load factor of the latter. In the embodiment described, each elevon of an aircraft is operated by two hydraulic motors in parallel with interconnected control means, and one such motor is associated with an electric motor, as in Fig. 2. The pump supplying the hydraulic motors has a pressure regulator, so that the fluid supplied is never at a greater pressure than that which exerts the maximum allowable torque on the elevon. In Fig. 2, control cables 3 pass around pulleys 21, 22 on a lever 20 to move shaft 19 fast with the lever and pivoted by levers 17 on to supports 18. A lever 24 fast to shaft 19 operates the valve rod of a piston and cylinder servomotor of which the piston-rod is pivoted to the aircraft framework and the cylinder operates the surface in well-known manner. Cables 10 interconnect the two hydraulic units. An electric motor and gear assembly 60 drive a pulley 61, cable 62, and a quadrant 64 which rotates the eleven on its axis, and also a feed-back quadrant 59 which drives a pulley 56, pulley 52, and cable 50. As shown in Fig. 3, cable 50 is attached to a sector 44 rotating coaxially with pulley lever 20 and having a camguide 45 with indented ends 47. A plate 40 mounted on shaft 19 bears two micro-switches 41a and 41b whose plungers are operated by rollers 43 contacting the cam guide 45. Operation of the control rocks shaft 19 about its supports, which causes one or other of rollers 43 to leave the indent 47 and be pressed in by surface 46, to operate one or other microswitch to actuate the motor in one or other sense, until the follow-up quadrant has rotated far enough to operate cable 50 to rotate sector 44 to bring both indents to engage the rollers. The torque limiter is shown in Fig. 6, the motor shaft 81 meshing with pinions 82 engaging the inner teeth of a gear ring 85, whose outer teeth engage a rack 87 normally centred by a strong doubleacting spring 93. In operation, the spring is sufficiently strong to prevent gear-ring 85 from moving. If the torque of shaft 81 rises above a certain limit, however, ring 85 will rotate and operate rack 87 in one direction or another, to operate one of microswitches 104 or 107, which are wired in series with switches 41a and 41b as overload cut-outs, and also operate warning lamps. A microswitch III actuated by displacement of the rack in either direction disconnects a clutch in the motor drive. A circuit is also described, Fig. 4 (not shown), wherein fall in pressure in the hydraulic circuit automatically operates a switch in the electric motor circuit to render the electric motor operable, and a failure in the electric circuit operates a solenoid valve to render the hydraulic circuit operable. When not operable, a brake is applied to the motor and its clutch disengaged, and the hydraulic circuit is. shut off from the servomotor. The pilot may select the hydraulic or electric circuit as operative.